The use of conventional radiation insensitive thermosetting resins for coating compositions is sometimes undesirable because of the necessity for thinning the resins with solvents to provide easy application to substrates. The use of solvents is costly as the solvents do not go into the final cured coating and must be removed from the coating composition. The removal of solvent, of course, also involves a pollution problem.
To alleviate the above problems, ionizing irradiation sensitive and actinic light sensitive materials have been developed. These radiation sensitive materials are ethylenically unsaturated monomers which cure by ionizing irradiation or actinic light to form coatings wherein essentially all of the material goes into the cured coating or film. In other words, essentially no solvents are necessary. The problem with these coatings is that in many cases the coating cured in this manner is not flexible and the properties of these coatings cannot be easily modified to meet the requirements of some end uses as can the conventional radiation insensitive thermosetting resins.
It has now been discovered that radiation sensitive liquid materials may be used as thinners for conventional radiation insensitive thermosetting resins. A mixture of the radiation sensitive material and radiation insensitive thermosetting resin may be subjected first to radiation to crosslink the radiation sensitive material and then to moisture, oxidation or heat to crosslink the radiation insensitive thermosetting resin. Alternatively, the mixture may be subjected first to moisture, oxidation or heat to crosslink the radiation insensitive thermosetting resin and then to radiation to crosslink the radiation sensitive material.
During exposure of the mixture to radiation, the degree of crosslinking of the radiation sensitive material is usually substantially complete. During exposure to moisture, oxidation or heat, the degree of crosslinking of the radiation insensitive thermosetting resin is usually substantially complete. When considered from the standpoint of the mixture, it may be said that the mixture is partially cured during the first exposure and completely cured after the second exposure.
Films of the mixture which are subjected to the dual exposures described above form flexible, abrasion resistant films. In some systems the radiation sensitive material and the radiation insensitive thermosetting resin interreact during one or both of the exposures. In other systems the radiation sensitive material and the radiation insensitive thermosetting resin do not interreact during either exposure.
The radiation sensitive coating materials may be any radiation curable organic materials. The most useful radiation sensitive organic materials are polyester resins and acrylic resins.
The polyester resins comprise unsaturated polyesters, solubilized in vinyl monomers. The unsaturated polyesters are ordinarily prepared from alpha-beta ethylenically unsaturated polycarboxylic acids and polyhydric alcohols.
The ethylenically unsaturated polycarboxylic acids include such acids as:
maleic acid PA1 fumaric acid PA1 aconitic acid PA1 mesaconic acid PA1 citraconic acid PA1 itaconic acid PA1 hydroxypivalyl mono(hydroxypivalate) PA1 ethylene glycol PA1 diethylene glycol PA1 triethylene glycol PA1 polyethylene glycol PA1 propylene glycol PA1 dipropylene glycol PA1 polypropylene glycol PA1 glycerol PA1 neopentyl glycol PA1 pentaerythritol PA1 trimethylol propane PA1 trimethylol ethane PA1 succinic acid PA1 adipic acid PA1 suberic acid PA1 azelaic acid PA1 sebacic acid PA1 isophthalic acid PA1 terephthalic acid PA1 tetrachlorophthalic acid PA1 styrene PA1 alpha-methylstyrene PA1 divinylbenzene PA1 diallyl phthalate PA1 methyl acrylate PA1 methyl methacrylate PA1 hexyl acrylate PA1 octyl acrylate PA1 octyl methacrylate PA1 diallyl itaconate PA1 diallyl maleate
and halo and alkyl derivatives of such acids and the like; the preferred acid being maleic acid. The anhydrides of these acids, where the anhydrides exist, are, of course, embraced under the term "acid", since the polyesters obtained therefrom are essentially the same whether the acid or anhydride is utilized in the reaction. The ethylenically unsaturated dicarboxylic acids are conventionally employed in an amount of about 10 mol percent to about 100 mol percent, although preferably in an amount of about 20 mol percent to about 80 mol percent of the total mols of acid component in the polyester.
The polyhydric alcohols useful in preparing unsaturated polyesters include:
and the like. The preferred polyols for the purposes of this invention have a molecular weight of less than about 2000 and consist essentially of carbon, hydrogen and oxygen. The polyhydric alcohols are generally employed in an equal molar-ratio to the total acid components, or as an excess, as, for example, about 20 mol percent excess.
Saturated dicarboxylic acids may be utilized in combination with the unsaturated acid or anhydride in the preparation of unsaturated polyesters. Such acids increase the length of the polyester without adding additional crosslinking sites, which is a desired feature in some polyesters. Examples of useful dicarboxylic acids which are either saturated or only aromatically unsaturated include:
and the like. As in the case of the ethylenically unsaturated acids, the anhydrides of these acids, where the anhydrides exist, are, of course, embraced in the term "acid", since the polyesters obtained therefrom are the same. Furthermore, for purposes of the present invention, the aromatic nuclei of such acids as phthalic acid are generally regarded as saturated since the double bonds do not react by addition, as do ethylenic groups. Therefore, wherever, the term "saturated dicarboxylic acid" is utilized, it is to be understood that such term includes the aromatically unsaturated dicarboxylic acids. Such "saturated carboxylic acids" may also be referred to as "non-olefinically unsaturated" polycarboxylic acids.
Vinyl monomers which crosslink with unsaturated polyesters to form thermosetting materials may be interpolymerized with the acrylic compounds and polyesters, if desired. Such vinyl monomers may include:
and the like. The preferred vinyl monomers are liquid compounds, soluble in the polyester components. Such monomers should preferably be free of non-aromatic carbon-carbon conjugated double bonds. The vinyl monomer as exemplified in the above list may be employed over a broad range. The amount of monomer should be sufficient to provide a liquid, flowable, interpolymerizable mixture. Ordinarily, the percentage of monomer will fall within the range of about 10 percent to about 60 percent by weight of the total mixture of polyester and monomer.
The preferred polyester resins are those formed from polyesters of propylene glycol or neopentyl glycol as the diol and maleic acid and adipic acid as the carboxylic acids with styrene or diallyl phthalate or vinyl toluene as the solubilizing monomer.
The acrylic compositions which may be used as the radiation sensitive materials in this invention may be esters or amides of acrylic or methacrylic acid or comonomers of such an ester with another copolymerizable monomer. Suitable esters include those of alcohols containing 1 to 8 carbon atoms such as methyl acrylate, methyl methacrylate, hydroxy ethyl acrylate, butyl methacrylate, octyl acrylate, and 2-ethoxy ethyl methacrylate. suitable amides include butoxymethyl acrylamide, methacrylamide, tertiary butyl acrylamide and other low melting alkyl acrylamides. Mixtures of such esters or amides may be copolymerized or one or more of the esters may be copolymerized with a higher alkyl ester or amide of acrylic or methacrylic acid or with another monomer containing a copolymerizable vinyl group, for example, itaconate esters, maleate esters, and allyl compounds. Alkylene dimethacrylates and diacrylates, such as 1,3-butylene dimethacrylate, and the like, and triacrylates and trimethacrylates, such as trimethyl propane trimethacrylate, and the like, may also be used. The preferred acrylates are polyacrylates and methacrylates, such as diacrylates, di-methacrylates, tri-acrylates, tri-methacrylates, and the like, such as acryloxypivalyl acryloxypivalate, bis-(acryloxyethyl) hexahydrophthalate and polymers thereof, bis-(acryloxyethyl) phthalate, and the like. Examples of these materials are found in U.S. Pat. No. 3,455,802 and British Pat. Nos. 1,162,722 and 1,162,721. The preferred materials are ethylenically unsaturated acrylic monomers.
The conventional thermosetting resins, which are not very radiation sensitive or actinic light sensitive, are those materials which normally cure by either oxidation, moisture, or heat, such as radiation insensitive polyurethane, radiation insensitive alkyds, radiation insensitive polyepoxides, radiation insensitive thermosetting acrylics, radiation insensitive aminoplast resins, and radiation insensitive Epon esters. Examples of the radiation insensitive thermosetting resins that may be used are given below: